NM prevents mount of network filesystem when jumbo frames are configured

I am exploring if I have hit a Network-Manager bug or I am overlooking something in the network configuration.

I am configuring jumbo frames on the eth0 network to improve performance on the connection to my NAS. When I disable Network-Manager and configure the network for auto startup, it works fine. I can confirm the jumbo frames work in my network because my network performance to my NAS almost doubles, and the ifconfig command confirms the MTU of 9000.

But with Network-Manager configured to start the network, nfs and cifs configured filesystems fail to mount. This failure to mount will still occur if I disable the mounting at boot and mount them after the system is up. The mount command will hang for many minutes, then time out.

I am on Ubuntu 14.04

Here are my network config files that don't allow the filesystems to mount:
/etc/network/interfaces:
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback
# iface eth0 inet dhcp
------
Relevent info in /etc/dhcp/dhclient.conf:
option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;
send host-name = gethostname();
default interface-mtu 9000;
supercede interface-mtu 9000;

request subnet-mask, broadcast-address, time-offset, routers,
 domain-name, domain-name-servers, domain-search, host-name,
 dhcp6.name-servers, dhcp6.domain-search,
 netbios-name-servers, netbios-scope,
 rfc3442-classless-static-routes, ntp-servers,
 dhcp6.fqdn, dhcp6.sntp-servers;
-----
I disabled NM by adding the word 'manual' to the file /etc/init/network-manager.override
I enabled the network with the following interfaces file:
# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo eth0
iface lo inet loopback
iface eth0 inet dhcp
--------------
I have a Wireshark trace file that shows a strange result I don't understand, if you think it will be helpful.

I would like to know: Does this look like a bug or have I missed something in enabling jumbo frames.
I would be glad to provide more info if it will help.